Because vehicle exhaust generates a large percentage of air pollutants, particularly in major cities, several state, municipal and federal government agencies regulate the emissions produced by certain vehicles. The United States Environmental Protection Agency (EPA) and the California Air Resources Board (CARB) are examples of government agencies currently regulating vehicle emissions. The On Board Diagnostic (OBD2) regulations promulgated by the EPA, for example, not only limit the amount of emissions legally produced by a vehicle, but also require that each vehicle monitor the emissions produced and issue a notification to the driver if emissions exceed a specified threshold. Vehicle emissions that are commonly regulated include carbon monoxide (CO), hydrocarbons/volatile organic compounds (VOCs) and nitrogen oxides (NOx).
Generally, automobiles and other vehicles are equipped with catalytic converters or other devices to reduce emissions produced by the engine. Catalytic converters reduce emissions by exposing exhaust from the engine to one or more chemical catalysts to reduce various pollutants to relatively harmless substances such as nitrogen, carbon dioxide and water. A conventional catalytic converter typically includes a reduction catalyst such as platinum or rhodium to reduce NOx emissions, as well as an oxidation catalyst such as platinum or palladium. Unburned VOCs and carbon monoxide are typically reduced by burning the materials in the presence the oxidation catalyst.
Oxygen for the catalytic burning process is typically obtained from the vehicle exhaust itself by controlling the air-to-fuel mixture provided to the engine. Oxygen may be further stored within the catalytic converter by ceria, cerium oxide or another catalyst material. The ability of a catalyst to store oxygen during periods of lean fuel mixture and to release the oxygen during periods of rich fuel mixture is referred to as the “oxygen storage capacity” of the converter. Oxygen storage capacity (OSC) may be measured by comparing the amounts of oxygen present in the gases entering and leaving the catalytic converter. Because the OSC tends to degrade as the catalysts age, OSC is generally considered to be a good indicator of catalytic converter effectiveness.
Many vehicles, particularly those equipped with V-6, V-8 and other relatively large engines, increasingly feature multi-banked exhaust systems. A multi-banked exhaust system includes multiple exhaust paths (i.e., “banks”) emanating from different cylinders in the engine. A dual-exhaust system, for example, typically includes two separate banks, each emanating from one bank of cylinders. Each bank typically includes its own catalytic converter, muffler and tailpipe such that exhaust gases from each bank are kept separate from those in the other banks until the gases are expelled from the vehicle. Difficulty frequently arises, then, in monitoring the total emissions of the vehicle, since no single point of measurement typically exists in a multi-banked system. Because most government regulations limit the amount of emissions on a per-vehicle basis instead of a per-bank basis, a conversion is needed between bank measurements and total vehicle emissions.
Accordingly, it is desirable to create an emissions diagnosis technique for multi-banked vehicle exhaust systems. In addition, it is desirable to create a multi-banked exhaust system that is capable of monitoring emissions from each bank. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.